Hi,
I want to build a LED constant current regulator to drive 7 LEDs, with a combined forward voltage 16.1V (OSRAM CP7P, @600mA). I tried to set the toff time to 295ns (Roff = 7.5k; Coff=470p), (I would like to modulate the EN pin ~ 2kHz)
However, the circuit produces a much higher off time, and noise peaks arise, while the IC is off. (the same noise is visible at Vout, PGATE...)
According the datasheet, the voltage at the Coff pin should be trimmed @1.24V. I measured the voltage there (10x probe, PicoScope 5000 series). As the image shows, it goes up to 7V (hence toff >2us)
Are there any external components (passive, power supply,...), which influence the voltage limit? What part of the circuit could be responsible for the noise peaks?
I appreciate any help, as this is my first experience with LED drivers.